1. Field
This invention generally relates to digital signal processing circuits, and more particularly to multirate digital signal processing circuit architectures.
2. Related Art
Digital signal processing applications, which operate on a sequence of discrete time sampled signal values, are sometimes able to more effectively be implemented with algorithms that process data with a sampling rate different than the initially captured rate. Fractional resampling is a process that receives an input data sequence that is sampled at a first, or input, sample rate and produces an output data sequence that also represents the input data sequence but that has an output sampling rate different that is different than the input sample rate. Fractional resampling generally operates to produce an output sample rate that is related to the input sample rate by an arbitrary, but pre-determined, fraction or ratio that is typically represented as p/q. The resampling ratio p/q indicates that for each “q” input samples, the resampling process produces “p” output samples. Undesirable aliasing in the output data sequence is often handled by a Finite Impulse Response (FIR) low-pass filtering process at an appropriate point in the resampling process.
Some conventional methods of fractional resampling utilize an FIR resampling filter with a filter length that is greater than the number of samples for the given rate change. Such a filter does not predicatively generate output samples beyond its own filter length. For certain scenarios when q is much greater than p, the filter length can become large. An alternative to a single resampling filter incorporates a series of m filters, where the resampling rate for each filter of is, for example (q−1)/q. Some resampling processes incorporating these conventional designs incorporate one or both of these alternatives.